What causes a root canal?!

Root Canal Treatment is where the canal of a tooth is cleaned treated and the nerve removed and replaced with a fake nerve made of a Paper point. When decay is deep enough and not able to be eased with a filling it is then found that the decay has went into the nerve and killed it off. The nerve that is dead then is full of bacterias and constantly gets sore and tender due to bacteria build up. The canal is then drilled to widen it, cleaned out and lined with an antibacterial paste, it is then rinsed out with a sterile solution such as Milton and then packed in with a GP point which is a Gutcha Pertcha Point, a fake nerve. The hole in the tooth is then sealed with a filling. This normally solves the pain and decay developing.

I am a dental nurse in UK

When the nerves in teeth die, that weakens the teeth significantly. A root canal is done to dig out the rotted nerve. I am not sure why a rotted nerve in the teeth would be a problem. However there is always Wikipedia!

http://en.wikipedia.org/wiki/Root_canal
"For many people who experience tooth pain or discomfort, a root canal may be recommended, and a qualified dentist or more preferably an endodontist (root canal therapy specialist) should be consulted in a timely manner."